Over the past few years the dramatic increase in the use of fiber optics in communications systems has created a tremendous need for both cheaper and more reliable optical components. Unfortunately, the limited materials usable to create acceptable laser diodes and photo detectors for use in such devices effectively limits the mean time between failures (MTBF) that can be achieved for such devices.
Typically diode lasers or photodetectors are fabricated by growing the devices on a semiconductor substrate. Depending upon the particular devices and there design, this may entail the use of known techniques such as liquid-phase epitaxy, metal-organic vapor-phase epitaxy, molecular beam epitaxy. Each of these techniques has its advantages and disadvantages in terms of the quality, reliability, and frequency of defect occurrence.
Once the active portion of the device is produce by the epitaxial growth process, the devices are then further processed into device chips. During these processes dielectric films and various metals are deposited on the semiconductor, for example, to isolate parts or create contacts. Finally, photolithography and/or chemical or physical etching are used to finish the devices. Once the device structures are fully formed in the semiconductor wafer, each device is separated from the wafer, for example, by cleaving.
FIGS. 1A and 1B show two variants of an example optical device of the prior art, a semiconductor laser diode. The specific devices 110, 120 shown in FIGS. 1A and 1B are vertical cavity surface emitting lasers (VCSEL). As shown, each device 110, 120 is contained in an approximately 200 micrometer (micron) square area of semi-conductor material. Each device 110, 120 has an optical window 112, 122 of approximately 17-19 micron diameter. The device 110, 120 is connected via a trace 114, 124 to a bonding pad 116, 126 approximately 100 microns square. In FIG. 1A, the bonding pad serves as the positive (“+”) contact and in FIG. 1B, the bonding pad serves as the negative (“−”) contact.
FIG. 2 shows multiple individual VCSELs that have been combined to form at least a 2×3 array of lasers. The devices 200 are arranged so that the spacing between each laser (i.e. the “pitch”) is approximately 250 microns. Such arrays can be relatively reliable, because each individual laser device 200 can be operationally tested before it is integrated into the array. However, once the array is created, if an individual element fails, either the entire array must be replaced or the array becomes degraded because there is no easy way to repair it.
Moreover, even if the array is created from macrostructures, for example, so that there are 1×4 discrete devices on a common carrier. If any one of the devices is defective, the entire carrier becomes useless or the individual good devices must be removed from it and used individually.
All of the above results in arrays that are both costly to produce and, in their overall configuration, have an overall MTBF of the least reliable device in the array.
Thus there remains a need in the art for a way to produce a chip incorporating an array of optical devices that is less costly to produce.
There remains a further need in the art for an array that is easy to repair at low cost.